This invention relates to a cylinder head gasket assembly, and more particularly to a gasket having an embossment surrounding, and immediately adjacent to, the combustion openings in the gasket assembly. The embossment is filled with expanded graphite and produces an enhanced heat-resistant seal for the engine cylinder.
Gaskets are widely used for providing seals between pairs of confronting surfaces, such as between engine blocks and heads in internal combustion engines, and the like. Gaskets used in such applications must provide an effective seal between the relatively large number of interconnecting cavities carrying fluids of different types and under different pressures so that the fluids do not intermingle or leak externally. Such gaskets frequently incorporate a metallic core and compressible facings and are provided with special sealing means at the cylinder openings. In some such gaskets one or more sealing embossments surrounding the cylinders are provided in the metallic core. Such embossments provide projections on the body of the gasket. One purpose is to provide a smaller area of contact between the gasket and the confronting surfaces, thereby to increase the compression force per unit area, hence to generate a more effective seal. U.S. Pat. No. 3,352,564 to Johnson discloses a gasket having typical embossments which are formed by deforming the metal body, as around cylinder openings, so the gasket body is deflected upwardly and downwardly from the plane of the surrounding gasket metal. An embossment made in this manner includes a raised portion or projection, and defines a corresponding indented portion or recess on the other side of the projection.
One of problems encountered with gaskets having embossments of the kind typified by those shown in the Johnson patent is that the embossments flatten under compression. When this occurs, the load which was intended to be concentrated in the zone of the embossment tends to be distributed over a much broader surface of the gasket, consequently lowering the effectiveness of the seal. Further the flattening tends to be inelastic so that the seal can be ineffective for that reason alone.
Further, such embossments adjacent the combustion cylinders, such as at the combustion openings of gaskets (such as shown in U.S. Pat. No. 4,325,559) are subject to great stresses and high temperatures. In some such gaskets, such temperatures and stresses gradually tend to reduce the effectiveness of the seal. Thus, even if fillers, such as the elastomeric fillers of the types referred to in U.S. Pat. No. 4,140,323 are used, when used adjacent the combustion opening they tend to degrade and thus the effectiveness of the seal tends to diminish in use.
Cylinder head gaskets in which embossments have been suggested for use include those disclosed in the above-mentioned U.S. Pat. No. 4,325,559, as well as in British Pat. No. 899,552 which discloses the use of a lacquer and flake graphite as a filler therefor and in German Pat. No. 819,177 in which various fillers are described for use in the recesses of embossments. Further, gaskets, such as those used for pipe flanges (in which stresses, repeated dynamic loading and temperature concerns are of relatively little concern as compared to automotive head gasket applications) and having annular embossments filled with a deformable elastomeric sealing material are shown in Black U.S. Pat. No. 3,721,452. It has also been suggested that an expanded graphite material be used as a filler in similar pipe flange sealing gasket embossments. Finally, expanded graphite material, such as Calagraph referred to hereinafter, has been suggested for use in high temperature, high stress applications, such as automotive applications. Calagraph is sold by Calcarbon, a division of Polycarbon, Inc. having offices in Chatsworth, California.